Field of the Invention
Embodiments of the present invention relate generally to an inspection method for a blanking device for blanking multi charged particle beams, and more specifically, to an inspection method for a blanking device to be placed (mounted) in a multi-beam writing apparatus, for example.
Description of Related Art
The lithography technology that advances miniaturization of semiconductor devices is extremely important as a unique process whereby patterns are generated in semiconductor manufacturing. In recent years, with high integration of LSI, the linewidth (critical dimension) required for semiconductor device circuits is decreasing year by year. The electron beam (EB) writing technique, which intrinsically has excellent resolution, is used for writing or “drawing” a pattern on a photomask blank, etc. with electron beams.
As an example employing the electron beam writing technique, a writing apparatus using multiple beams (multi-beams) can be cited. Compared with the case of writing a pattern by using a single electron beam, since it is possible to emit multiple beams at a time (one shot) in multi-beam writing, the throughput can be greatly increased. For example, in a writing apparatus employing a multi-beam system, multi-beams are formed by letting portions of an electron beam emitted from an electron gun assembly pass through a corresponding hole of a plurality of holes in the mask, a blanking control is provided for each of the beams, and each unblocked beam is reduced by an optical system and deflected by a deflector so as to irradiate a desired position on a target object or “sample”.
In multi-beam writing, the dose of each beam is separately controlled based on an irradiation time. For highly accurately controlling such a dose of each beam, it is necessary to perform high speed blanking control to provide an ON or OFF state of each beam. In a writing apparatus of a multi-beam system, a blanking control circuit for each beam is placed on a blanking plate where blankers each for each of multi-beams are arranged.
Here, each blanker for the multi-beams is configured by a pair of counter electrodes, and specifically, a voltage for blanking control is applied to a control electrode and the other counter electrode is grounded (earthed). In blanking control, a beam OFF state is generated by applying a positive potential to the control electrode, and a ground potential to the grounded counter electrode in order to deflect a beam toward the control electrode, so as not to let the beam pass through a limiting aperture of the blanking aperture member placed below the blankers. For example, when multi-beams are composed of n×n beams, n×n pairs of electrodes and their control circuits are arrayed in the blanking device. For example, with respect to a blanking device in which 512×512 pairs of electrodes and their control circuits are arrayed, it is reported that the fraction defective of the structure that is configured by the 512×512 pairs of electrodes and their control circuits is about 0.04%. As one of defects, there is a case in which a short circuit (short) has occurred between the electrodes by some malfunction. In such a case, a problem is generated in that since it is impossible to control ON/OFF of the beam, the blanking control function cannot be achieved. Moreover, as another of defects, there is a case in which the electrode is in a floating state due to a disconnection (open), etc. between the control circuit and the control electrode by some malfunction. Also, in such a case, a problem is generated in that since it is impossible to control ON/OFF of the beam, the blanking control function cannot be achieved. With respect to such defects of the structure produced by pairs of electrodes and their control circuits, it is conventionally difficult to check the beam control state before actually placing the blanking device in the writing apparatus and emitting each beam of the multi-beams. Moreover, even if performing an inspection after placing the blanking device in the writing apparatus, since the number of beams is enormous, the inspection will take time. Furthermore, if, after placing the blanking device in the writing apparatus, it turns out that the blanking device is unusable, it will be troublesome to perform exchange, etc.
Conventionally, as another defect, there is a problem in that when the beam state is fixed to ON, it becomes out of control. Then, a method is examined in which, before beams including such a defective beam irradiate the target object, a movable block member is transferred to be directly underneath the beams in order to compulsorily perform blocking (e.g., refer to Japanese Patent Application Laid-open (JP-A) No. 2013-128031).
However, conventionally, no efficient method has been established to inspect, at a stage before placing a blanking device in a writing apparatus, whether a beam defect is to occur in the system or not.